Method of regulating the outlet flow of a liquid separated in a centrifugal separator and a centrifugal separator to carry out the method

ABSTRACT

Method in a centrifugal separator of regulating during operation the outlet flow through a stationary discharge device, which is arranged in an outlet chamber, of a separated liquid and a centrifugal separator to carry out the method. In order to accomplish a method and a centrifugal separator, which makes it possible to regulate the outflow of a liquid, which is separated in a centrifugal separator and discharged out of the same through a stationary discharge device within a wide flow range with small energy losses and with a small risk of rotor dynamical oscillations this outlet flow is regulated by bringing at least a portion of the separated liquid present in the outlet chamber (12) to rotate at a lower angular speed than the rotor in an angular zone (24) of the outer chamber, which is free from elements rotating with the rotor, and in which the inlet opening (19) is located, and by bringing liquid, which is present in this zone (24), to flow through at least one passage (26), which is delimited by elements (25) rotating with a rotor and which has an inlet (35) and an outlet (37) located outside this inlet (35) in the outlet chamber (12), when the free liquid surface is located radially inside a predetermined radial level (27), at which the inlet (35) of the passage is located.

FIELD OF THE INVENTION

The present invention concerns a method of regulating during operationthe outlet flow of a liquid separated in a separation chamber in a rotorof a centrifugal separator, the rotor being rotatable around therotational axis in a predetermined rotational direction, in which methodthe separated liquid is conducted into an outlet chamber and is broughtto form a rotating liquid body in the outlet chamber with a radiallyinwardly directed free liquid surface and is discharged out of theoutlet chamber through a stationary discharge device, which has at leastone internal outlet channel with an inlet opening in a radially outerpart of the discharge device, which during operation is located radiallyoutside the free liquid surface.

Furthermore, the invention concerns a centrifugal separator, in whichthe outlet flow of a separated liquid is regulated according to thismethod. Such a centrifugal separator comprises a rotor, which isrotatable around a rotational axis in a predetermined direction andforms an inlet chamber for a liquid to be centrifugally treated, aseparation chamber, which is connected to the inlet chamber, and anoutlet chamber, which is delimited axially by two end walls and radiallyby a circumferential wall connecting these end walls and is arranged toreceive during operation a liquid separated in the separation chamber,the outlet chamber being so designed that the liquid present in the sameforms a rotating liquid body having a radially inwardly directed freeliquid surface. The rotor also forms a connection, which is arrangedthrough one of said end walls and has an opening in the outlet chamberlocated radially inside the radial level of the free liquid surface. Theoutlet chamber communicates through this connection with the separationchamber. The centrifugal separator also comprises a stationary dischargedevice, which is arranged in the outlet chamber and has at least one toan outlet connected outlet channel with an inlet opening in a part ofthe discharge device, which is located radially outside the free liquidsurface.

BACKGROUND OF THE INVENTION

A centrifugal separator of this kind is shown in WO 89/03250. Duringoperation of the shown centrifugal separator the liquid present in theoutlet chamber is entrained gently into the rotation of the rotor bymeans of discs, which are arranged in the outlet chamber. The separatedliquid is discharged out of the outlet chamber through a stationarydischarge device arranged therein, which is connected to an outlet. Theflow of the discharged liquid depends on the angular speed of therotating liquid in the outlet chamber, the radial position of the freeliquid surface, the design of the discharge device, and the prevailingcounter pressure in the outlet for the liquid.

For every use of such a centrifugal separator a discharge device ischosen having for the actual case a suitable flow capacity range, whichis limited for one and the same discharge device. Within the flowcapacity range the flow is regulated by adjusting the counter-pressurein the outlet. If the actual flow of the separated liquid is low thecounter-pressure from the equipment connected to the outlet often isinsufficient and an extra counter-pressure has to be imposed at theoutlet, which means energy losses. Besides, a low flow through thedischarge device often results in an unstable flow, which in turn givesrise to rotor dynamical oscillations.

SUMMARY OF THE INVENTION

The object of the present invention is to accomplish a method and acentrifugal separator of the kind initially described, which makes itpossible to regulate the outlet flow of the liquid, which is separatedin a centrifugal separator and is discharged out of the same through astationary discharge device within a wide flow range with small energylosses and with a small risk of rotor dynamical oscillations.

According to the present invention this is accomplished by the fact thatthe outlet flow discharged through the discharge device is regulated bybringing at least a portion of the separated liquid present in theoutlet chamber to rotate at a lower angular speed than the rotor in anannular zone of the outlet chamber, which coaxially surrounds therotational axis and is free from elements rotating with the rotor, andin which the inlet opening is located and by bringing the liquid presentin this zone to flow through at least one passage, which is delimited byelements rotating with the rotor and has an inlet and a radially outsidethis inlet located outlet in the outlet chamber, when the free liquidsurface is located radially inside a predetermined radial level, atwhich the inlet of the passage is located.

Hereby the separated liquid present in the outlet chamber is entrainedeffectively and the discharge capacity of the discharge device isincreased at first when the free liquid surface is located radiallyinside the predetermined radial level and there is a need for anincreased outlet flow.

In a preferred embodiment of the invention the separated liquid isconducted into the outlet chamber radially inside the free liquidsurface and the liquid entered the outlet chamber is brought to flowradially outwardly towards the free liquid surface through channelsalong and in contact with the surface of a wall element, the surfacedelimiting the channel forwardly seen in the rotational direction andextending radially, axially and in the circumferential direction andbeing curved in a plane perpendicular to the rotational axis with acenter of curvature, which at each point of the surface is locatedbehind the surface seen in the rotational direction, and has a radius ofcurvature, which at essential each point of the surface is smaller thanthe radius of curvature of an involute, along which separated liquidfreely strives to move radially outwardly relative to the rotor at theradius at which said point is located.

By bringing the separated liquid to rotate at a lower angular speed thanthe rotor in this manner at least a portion of the kinetic energy, whichthe separated liquid possesses when it enters the outlet chamber, isreused to operate the rotor.

A centrifugal separator of the kind initially described according to thepresent invention is designed with a discharge device, in which theinlet opening of the outlet channel is located in an annular zone of theoutlet chamber, which surrounds the rotational axis and is so big andfree from elements rotating with the rotor that liquid is admitted torotate at an essential lower angular speed than the rotor. Furthermore,according to the invention a device is arranged in connection with theoutlet chamber to bring at least a portion of the liquid which ispresent in this zone of the outlet chamber, during operation to rotateat a lower angular speed than the rotor, and elements rotating with therotor are arranged to form at least one passage, which has an inletlocated in the outlet chamber at a predetermined radial level radiallyinside the inlet opening of the outlet channel and an outlet locatedradially outside this radial level in a way such that the separatedliquid is admitted to flow through this passage radially outwardlyduring entrainment of the same into the rotational rotor when saidliquid surface is located radially inside the inlet of the passage.

In order to make recovery of the kinetic energy of the separated liquidat its entrance into the outlet chamber possible, said device comprisesaccording to a preferred embodiment of the invention at least two wallelements, which are arranged in the outlet chamber fixedly connected tosaid one end wall and extend radially, axially and in thecircumferential direction. The wall elements are arranged to betweenthemselves form a channel for the flow of separated liquid which entersthe outlet chamber via said connection, radially outwardly towards thefree liquid surface. The channel is delimited forwardly seen in therotational direction by a surface of the wall element, at least a partof the surface extending radially between the opening of the connectioninto the outlet chamber and the free liquid surface and is curved in aplane perpendicular to the rotation axis with a centre of curvature,which at essentially each point of this part of the surface is locatedbehind the surface seen in the rotational direction, and with the radiusof curvature, which at each point of this part of the surface is smallerthan the radius of curvature of an involute, along which separatedliquid strives to move freely radially outwardly relative to the rotor,at the same radius as the radius at which the point is located.

In another embodiment of the invention a covering device is arranged inthe outlet chamber fixedly connected to each one of the wall elements ontheir axial ends turned from said one end wall and is arranged to atleast delimit a portion of the channel located closest to the connectionfrom the outlet chamber.

In a further embodiment of the invention said device for the energyrecovery forms at least two passages having inlets, which each one islocated at the predetermined radial level. The outlets of these twopassages then can be located at the same or at different radial levels.In a special embodiment of the invention this device comprises at leastone around the rotational axis extending angular disc, which has anopening extending radially outwardly towards the predetermined radiallevel. The opening in the disc is suitably circular and surrounding therotational axis concentrically.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described more closely withreference to the attached drawings, in which

FIG. 1 schematically shows an axial section through a part of acentrifugal separator according to the invention,

FIG. 2 schematically shows an axial section through a part of thecentrifugal separator shown in FIG. 1 according to an embodiment of theinvention,

FIG. 3 schematically shows a radial section through a detail of the partshown in FIG. 2, and

FIG. 4 schematically shows an axial section through a part of acentrifugal separator according to a modified embodiment of theinvention.

DETAILED DESCRIPTION

The part of a centrifugal separator according to the invention shown inFIG. 1 comprises a rotor, which has a lower part 1 and an upper part 2which are joined together axially by means of a locking ring 3. Insidethe centrifugal separator shown as an example there is arranged anaxially movable valve slide 4. This valve slide 4 delimits together withthe upper part 2 a separation chamber 5 and is arranged to open andclose an annular gap towards peripheral outlet openings 6 for asubstance, which during operation has been separated in the rotor andaccumulated at the periphery of the separation chamber 5. The valveslide 4 delimits together with the lower part 1 a closing chamber 7,which is provided with an inlet 8 and a throttled outlet 9 for a closingliquid.

Inside the separation chamber 5 a disc stack 10 is arranged consistingof a number of conical separation discs between a distributor 11 and theupper part 2. The upper part 2 forms at its in the figure shown upperend an outlet chamber 12, into which in this case a relatively light,separated liquid can flow from the separation chamber 5 via a centralpassage 13. The liquid present in the outlet chamber 12 during operationof the rotor forms a rotating liquid body having a radially inwardlyfree liquid surface 14.

Centrally through the outlet chamber 12 a stationary inlet tube 15extends, which opens into an inlet chamber 16 in the interior of thedistributor 11. Next to the inlet tube 15 a stationary outlet tube 17 isarranged for the specific lighter liquid in the chamber 12. An outletdevice 18 is arranged in the chamber around the inlet tube 15 andconnected to the outlet tube 17.

The outlet device 18 extends radially outwardly in the outlet chamber 12and has a portion located outside the radial level of the free liquidsurface 14. In the outlet device 18 at least one outlet channel 20 isarranged with an inlet opening 19 which is located in this portion ofthe discharge device. The outlet channel 20 is connected to the interiorof the inlet tube 17.

The outlet chamber is axially delimited by two end walls 21 and 22, theone 21 of which delimits the outlet chamber towards the separationchamber 5. The connection 13 is arranged centrally through this end wall21. Inside the outlet chamber 12 a device 23 is fixedly attached to thisend wall to bring during operation at least a portion of the liquid,which is present in the outlet chamber, to rotate at a lower angularspeed than the rotor. An annular zone 24 of the outlet chamber 12surrounding the rotational axis coaxially, in which the inlet opening ofthe outlet channels is located, is so big and free from elementsrotating with the rotor that liquid in this zone is admitted to flow atan essential lower angular speed than the rotor.

On the other end wall 22 elements 25 are fixedly attached to the rotorto form passages 26, through which liquid in the outlet chamber flowswhen the free liquid surface is located radially inside a predeterminedradial level 27. For this purpose the passages have inlets, which arelocated at the predetermined radial level 27, and outlets, which arelocated radially outside this radial level 27.

In FIG. 2 an outlet chamber 28 in a centrifugal separator according toan embodiment of the invention is shown in more detail. The device shownin this figure consist of wall elements 30 fixedly attached to the oneend wall 29, the wall elements extending radially, axially, and incircumferential direction and between themselves forming channels 31. Onthe side of the wall elements 30 turned from the end wall 29 an annularcovering device 32 surrounding the rotational axis are fixedly attached,which delimit the channels 31 axially from the outlet chamber 28. To theother end wall 33 elements 34 are fixedly attached, which form passageshaving an inlet 35 located at the predetermined radial level 36 andhaving outlets 37 located radially outside this level. The circular discshaped discharge device 38 arranged in the outlet chamber 28 is in itsradial outer portion surrounded by an annular zone 39 of the outletchamber 28 surrounding the rotational axis, which is free from elementsrotating with the rotor and is so big that liquid, which is locatedduring operation in this zone 39 of the outlet chamber 28, is admittedto rotate at a lower angular speed than the rotor.

In FIG. 3 there is shown a view from above of the wall elements 30 andthe channels 31 in FIG. 2. The channels 31 are in the shown exampleconverging radially outwardly and are delimited forwardly seen in therotational direction by a surface, which extends radially between theopening into the outlet chamber 28 of the connection 40 and the freeliquid surface and is curved in a plane perpendicular to the rotationalaxis with a centre of curvature, which for each point on the surface islocated behind the surface seen in the rotational direction, and with aradius of curvature, which for essentially each point on the surface issmaller than the radius of curvature of an involute, along whichseparated liquid strives to move freely radially outwardly relative tothe rotor, at the same radius, as the radius at which the point islocated.

In FIG. 4 an outlet chamber 41 in a centrifugal separator according toanother embodiment of the invention is shown. According to thisembodiment said device partly consists of wall elements 43 fixedlyattached to the end wall 42, which are of the same kind as the wallelements 30 shown in FIG. 3, and to which a covering device 44 isfixedly attached covering the channels (not shown) between the wallelements 43. To the axially opposite side of the covering device 44other wall elements 43 are fixedly attached, which between themselvesform other channels (not shown), which in turn are covered by a coveringdevice 44.

Centrally in the outlet chamber 41 a circular disc shaped dischargedevice 45 is arranged also in this embodiment, which in its radiallyouter part is surrounded by an annular zone 46 of the outlet chamber 41surrounding the rotational axis, which is free from elements rotatingwith the rotor and is so big that liquid, which is located duringoperation in this zone 46 of the outlet chamber, is admitted to rotateat a lower angular speed than the rotor.

On each axial sides of the discharge device 45 elements rotating withthe rotor are arranged in the outer chamber 41 in the shape of a numberof annular circular disc 47, which delimit passages 48 for the liquid,which is located during operation in the outlet chamber 41. Centrallyeach disc has a circular opening, the center of which coincides with therotational axis. The largest radii of the openings are equally big andform inlets 49 to the passages 48 at a predetermined radial level. Theoutlet 50 of the passages 48 are in this shown example located at aradius, which increases with the distance from the discharge device 45.

Upon start of the centrifugal separator the rotor is brought to rotateand the separation chamber 5 is closed by supplying a closing liquid tothe closing chamber 7 through the inlet 8. When the separation chamber 5is closed the liquid, which is to be centrifugally treated, can besupplied to the separation chamber through the inlet tube 15 and theinlet chamber 16. Eventually the separation chamber 5 is filled up, therotor obtains operational number of revolutions and the conditions arestabilized inside the separation chamber. The components in the suppliedliquid are separated during the influence of the centrifugal forcesacting on the same.

The separation is then mainly taking place in the spaces between theconical discs in the disc stack 10. During the separation the specificheavier component is thrown radially outwardly and is collected at theradially outermost part of the separation chamber, whereas a specificlighter liquid flows radially inwardly in these spaces.

The specific heavier component is discharged intermittently duringoperation by having the valve slide 4 to uncover the peripheral outletopenings 6 during time periods.

The specific lighter liquid flows out of the separation chamber 5through passages 13 to the outlet chamber 12, in which it forms arotating liquid body with a radially inwardly directed free liquidsurface. The liquid present in the outlet chamber 12 is dischargedthrough the outlet 19 and further out through the outlet channel 20 inthe stationary outlet device 18.

At least a portion of the liquid present in the outlet chamber, or asshown in the embodiment according to FIG. 2, 3 and 4 the liquid flowinginto the outlet chamber 28 and 41, respectively, is brought to rotate ata lower rotational speed than the rotor.

According to the embodiments shown in FIG. 2, 3 and 4 this is takingplace by the fact that the liquid entered the outlet chamber is broughtduring its radial movement radially outwardly towards the free liquidsurface to flow in channels, which seen forwardly in the rotationaldirection is delimited by a surface of the wall element 30 and 43,respectively. This surface is curved in a plane perpendicular to therotational axis with a central curvature, which for essentially eachpoint on this portion of the surface is located behind the surface seenin the rotational direction and with a radius of curvature, which foreach point on this portion of the surface is smaller than the radius ofcurvature of an involute, along which separated liquid strives to movefreely radially outwardly relative to the rotor, at the same radius, asthe radius at which the point is located.

Thanks to this design the liquid will flow radially outwardly along thissurface. The kinetic energy possessed by the liquid when it enters theoutlet chamber will hereby be reused at least partly to operate therotor.

Within the range of the present invention it is quite possible to bringliquid present in the outlet chamber to rotate at a lower angular speedthan the rotor in another way. For instance, the liquid can by differentdesign of channels in the separation chamber be given a lower angularspeed already before it enters the outlet chamber. Besides, the liquidflow into the outlet chamber can be directed in a way such that itsangular speed becomes lower than the rotor. Another alternative is torecirculate a portion of the liquid, which has been discharged by thestationary discharge device, to the outlet chamber.

What is claimed is:
 1. A method of regulating during operation theoutlet flow of a liquid separated in a separation chamber in a rotor ofa centrifugal separator, the rotor being rotatable around a rotationalaxis in a predetermined rotational direction, in which method theseparated liquid is conducted into an outlet chamber and is brought toform a rotating liquid body in the outlet chamber with a radiallyinwardly directed free liquid surface and is discharged out of theoutlet chamber through a stationary discharge device, which has at leastone internal outlet channel with an inlet opening in a radial outer partof the discharge device, said radial outer part during operation islocated radially outside the free liquid surface, wherein the separatedliquid is charged through the outlet channel with an outlet flow, whichis regulatedby bringing at least a portion of the separated liquidpresent in the outlet chamber to rotate at a lower angular speed thanthe rotor in an annular zone of the outlet chamber, which coaxiallysurrounds the rotational axis and is free from elements rotating withthe rotor, and in which the inlet opening is located, and by bringingliquid present in this zone to flow through at least one passage, whichis delimited by elements rotating with the rotor, said at least onepassage having an inlet and having an outlet located radially outsidethis inlet in the outlet chamber, when the free liquid surface islocated radially inside a predetermined radial level, at which the inletof the at least one passage is located.
 2. The method according to claim1, wherein the separated liquid is conducted into the outlet chamberradially inside the free liquid surface and in that the liquid enteredinto the outlet chamber is brought to flow radially outwardly towardsthe free liquid surface through channels along and in contact with asurface of a wall element in the outlet chamber, the surface delimitingeach channel forwardly seen in the rotational direction and extendingradially, axially and in the circumferential direction and being curvedin a plane perpendicular to the rotational axis with a center ofcurvature, which at each point on the surface is located behind thesurface seen in the rotational direction, and has a radius of curvature,which at essentially each point on the surface is smaller than theradius of curvature of an involute, along which separated liquid freelystrives to move radially outwardly relative to the rotor at the radius,at which said point is located.
 3. A centrifugal separator to carry outthe method according to claim 1, comprising a rotor, which is rotatablearound a rotational axis in a predetermined direction and formsan inletchamber for a liquid to be centrifugally treated, a separation chamber,which is connected to the inlet chamber, an outlet chamber, which isdelimited axially by two end walls and radially by a circumferentialwall connecting these end walls and is arranged to receive duringoperation a liquid separated in the separation chamber, the outletchamber being so designed that liquid present in the outlet chamberforms a rotating liquid body having a radially inwardly directed freeliquid surface, and a connection, which is arranged through one of saidend walls and has an opening in the outlet chamber located radiallyinside the radial level of the free liquid surface, and through whichconnection the outlet chamber communicates with the separationchamber,the centrifugal separator also comprising a stationary dischargedevice, which is arranged in the outlet chamber and has at least oneoutlet channel connected to an outlet, the outlet channel having aninlet opening in a part of the discharge device, which is locatedradially outside the free liquid surface, wherein the inlet opening islocated in an annular zone of the outlet chamber, which surrounds therotational axis and is so big and free from elements rotating with therotor that liquid is admitted to rotate at an essentially lower angularspeed than the rotor, a device is connected to the outlet chamber tobring at least a portion of the liquid, which is present in this zone ofthe outlet chamber, during operation to rotate at a lower angular speedthan the rotor, and elements rotating with the rotor are arranged toform at least one passage, which has an inlet located in the outletchamber at a predetermined radial level radially inside the inletopening of the outlet channel and an outlet located radially outsidethis radial level in a way such that separated liquid is admitted toflow through this passage radially outwardly during entertainment of theseparated liquid into the rotation of the rotor when said liquid surfaceis located radially inside the inlet of the passage.
 4. The centrifugalseparator according to claim 3, which further comprises at least twowall elements, which are arranged in the outlet chamber fixedlyconnected to said one end wall and extend radially, axially and in thecircumferential direction, and are arranged to form a channel betweenthemselves for the flow of separated liquid, which enters the outletchamber via said connection, radially outwardly towards the free liquidsurface, the channel being delimited forwardly seen in the rotationaldirection by a surface of one of the wall elements, at least a part ofthe surface extending radially between the opening of the connectioninto the outlet chamber and the free liquid surface, said wall elementsurface being curved in a plane perpendicular to the rotational axiswith a center of curvature, which at essentially each point on this partof the surface is located behind the surface seen in the rotationaldirection, and with a radius of curvature, which at each point on thispart of the surface is smaller than a radius of curvature of aninvolute, along which separated liquid strives to move freely radiallyoutwardly relative to the rotor, at the same radius as the radius atwhich the point is located.
 5. The centrifugal separator according toclaim 4, further comprising a covering device, which is arranged in theoutlet chamber fixedly connected to each one of the wall elements ontheir axial sides turned from said one end wall and is arranged todelimit at least a portion of the channel located closest to theconnection from the outlet chamber.
 6. The centrifugal separatoraccording to claim 3, wherein said elements form at least two passages,each having an inlet, each of which inlets is located at thepredetermined radial level.
 7. The centrifugal separator according toclaim 6, wherein the outlets of the passages are located at differentradial levels.
 8. The centrifugal separator according to claim 3,wherein said elements comprise at least one annular disc extendingaround the rotational axis having an opening extending radiallyoutwardly to the predetermined radial level.
 9. The centrifugalseparator according to claim 8, wherein the opening is circular andenclosing the rotational axis concentrically.